Recently, there has been a demand for easy-to-assemble fluid machines, and fluid machines in which a rotary shaft is efficiently assembled with a casing have been proposed (see Patent Documents 1 and 2).
The fluid machine disclosed in Patent Document 1 has a casing that is divided into two parts, or an upper casing member and a lower casing member. A rotary shaft is inserted through a ring (block body) with a bearing and a shaft sealing device. A protrusion protruding from the ring is fitted to a recess portion of the lower casing. Then, the upper casing member is assembled to the lower casing member to assemble the fluid machine.
The fluid machine disclosed in Patent Document 2 is a multistage vacuum pump. The vacuum pump has a casing including an upper casing member and a lower casing member, and a plurality of pump operation chambers are defined in the casing. A drive shaft and a driven shaft are each supported to the lower casing member with a bearing and a shaft sealing device. The drive shaft has a drive gear and a plurality of drive rotors, and the driven shaft has a driven gear and a plurality of driven rotors. The upper casing member is assembled to the lower casing member to assemble the fluid machine. Before the upper casing member is assembled to the lower casing member, a clearance between each rotor and an inner surface of a pump operation chamber is adjusted. An engagement position of the drive gear and the driven gear that are timing gears is adjusted to adjust the phase difference between the drive rotor and the driven rotor.
When the fluid machine disclosed in Patent Document 1 is assembled, the ring and the bearing are separated from the lower casing member after the rotary shaft is supported to the lower casing member with the ring. Similarly, when the fluid machine disclosed in Patent Document 2 is assembled, the bearing is separated from the lower casing member after the rotary shaft is supported to the lower casing member with the bearing. Further, in the fluid machine disclosed in Patent Document 2, if the bearing is separated from the lower casing member, the phase difference between the drive rotor and the driven rotor cannot be accurately adjusted. Therefore, in some cases, the upper casing member is assembled to the lower casing member with an inaccurate phase difference between the drive rotor and the driven rotor.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-349490    Patent Document 2: Japanese Laid-Open Patent Publication No. 4-132895